In the mass production of small individually wrapped packages of butter, margarine, soup paste, or the like it is important that the packages all contain the same amount of whatever viscous or pasty material they contain. Accordingly it is standard to provide feedback control for the dosing device that fills the individual portions into the container. Downstream of the filling station a weighing station is provided which compares the gross weights of the individual packages with a set point and produces on deviation an error signal that is used to adjust the dosing device to eliminate this deviation. Such a system has the considerable disadvantage that there is a considerable delay between the time the package is made up and when its weight is checked, so that if the machine is starting to produce, for instance, undersized portions, the correction at the doser takes place after quite a few packages, which must be rejected, have been made. This problem is even more critical when very small packages are being made, for instance individually packed butter patties.
In German patent document 3,232,185 filed Aug. 30, 1982 by E. Muller a system is described where a piston-type doser forces individual portions of a viscous or pasty material, in this case sausage meat or headcheese, into individual containers, here sausage casings. In this arrangement the back pressure on the piston operating the dosing device is monitored to determine the specific gravity of the material being dosed. From this parameter it is possible to reliably gauge the mass of the portion being dosed.
Such a system offers some advantages, but still does not lend itself readily to a fast-acting mass-production operation that produces a large quantity of small packages